J. Semicond. > Volume 34 > Issue 6 > Article Number: 063004

Development of aluminum-doped ZnO films for a-Si:H/μc-Si:H solar cell applications

Zhifang Lei , Guangyu Chen , Shibin Gu , Lingling Dai , Rong Yang , Yuan Meng , Ted Guo and Liwei Li ,

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Abstract: This study deals with the optimization of direct current (DC) sputtered aluminum-doped zinc oxide (AZO) thin films and their incorporation into a-Si:H/μc-Si:H tandem junction thin film solar cells aiming for high conversion efficiency. Electrical and optical properties of AZO films, i.e. mobility, carrier density, resistivity, and transmittance, were comprehensively characterized and analyzed by varying sputtering deposition conditions, including chamber pressure, substrate temperature, and sputtering power. The correlations between sputtering processes and AZO thin film properties were first investigated. Then, the AZO films were textured by diluted hydrochloric acid wet etching. Through optimization of deposition and texturing processes, AZO films yield excellent electrical and optical properties with a high transmittance above 81% over the 380-1100 nm wavelength range, low sheet resistance of 11 Ω/$\square$ and high haze ratio of 41.3%. In preliminary experiments, the AZO films were applied to a-Si:H/μc-Si:H tandem thin film solar cells as front contact electrodes, resulting in an initial conversion efficiency of 12.5% with good current matching between subcells.

Key words: aluminum-doped zinc oxidemagnetron sputteringtandem silicon thin film solar cell

Abstract: This study deals with the optimization of direct current (DC) sputtered aluminum-doped zinc oxide (AZO) thin films and their incorporation into a-Si:H/μc-Si:H tandem junction thin film solar cells aiming for high conversion efficiency. Electrical and optical properties of AZO films, i.e. mobility, carrier density, resistivity, and transmittance, were comprehensively characterized and analyzed by varying sputtering deposition conditions, including chamber pressure, substrate temperature, and sputtering power. The correlations between sputtering processes and AZO thin film properties were first investigated. Then, the AZO films were textured by diluted hydrochloric acid wet etching. Through optimization of deposition and texturing processes, AZO films yield excellent electrical and optical properties with a high transmittance above 81% over the 380-1100 nm wavelength range, low sheet resistance of 11 Ω/$\square$ and high haze ratio of 41.3%. In preliminary experiments, the AZO films were applied to a-Si:H/μc-Si:H tandem thin film solar cells as front contact electrodes, resulting in an initial conversion efficiency of 12.5% with good current matching between subcells.

Key words: aluminum-doped zinc oxidemagnetron sputteringtandem silicon thin film solar cell



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Chang P K, Lu C H, Yeh C H. High efficiency a-Si:H/a-Si:H solar cell with a tunnel recombination junction and a n-type μ c-Si:H layer[J]. Thin Solid Films, 2012, 520: 3684. doi: 10.1016/j.tsf.2011.12.083

[1]

Kuo S Y, Chen W C, Lai F I. Effects of doping concentration and annealing temperature on properties of highly-oriented Al-doped ZnO films[J]. J Cryst Growth, 2006, 287: 78. doi: 10.1016/j.jcrysgro.2005.10.047

[2]

Lee K E, Wang M, Kim E J. Structural, electrical and optical properties of sol-gel AZO thin films[J]. Curr Appl Phys, 2009, 9: 683. doi: 10.1016/j.cap.2008.06.006

[3]

Elm M T, Henning T, Klar P J. Effects of artificially structured micrometer holes on the transport behavior of Al-doped ZnO layers[J]. Appl Phys Lett, 2008, 93: 232101. doi: 10.1063/1.3040312

[4]

Jung K, Choi W K, Yoon S J. Electrical and optical properties of Ga doped zinc oxide thin films deposited at room temperature by continuous composition spread[J]. Appl Surf Sci, 2010, 256: 6219. doi: 10.1016/j.apsusc.2010.03.144

[5]

Yang W F, Liu Z G, Zhang F. Structural, electrical, and optical properties of transparent conductive Al-doped ZnO films prepared by RF magnetron sputtering[J]. Journal of Semiconductors, 2008, 29: 2311.

[6]

Agashe C, Kluth O, Schope G. Modified Thornton model for magnetron sputtered zinc oxide:film structure and etching behaviour[J]. Thin solid films, 2003, 442: 80. doi: 10.1016/S0040-6090(03)00949-0

[7]

Calnan S, Hupkes J, Rech B. High deposition rate aluminum-doped zinc films with highly efficient light trapping for silicon thin film solar cells[J]. Thin solid films, 2008, 516: 1242. doi: 10.1016/j.tsf.2007.06.006

[8]

Ellmer K. Magnetron sputtering of transparent conductive zinc oxide:relation between the sputtering parameters and the electronic properties[J]. J Phys D Appl Phys, 2000, 33: 17. doi: 10.1088/0022-3727/33/4/201

[9]

Zhang H F, Yang S G, Liu H F. Preparation and characterization of transparent conducting ZnO:W films by DC magnetron sputtering[J]. Journal of Semiconductors, 2011, 32: 043002. doi: 10.1088/1674-4926/32/4/043002

[10]

Hooh J, Kim K K, Seong T Y. Effects of deposition temperatures and annealing conditions on the microstructural, electrical and optical properties of polycrystalline Al-doped ZnO thin films[J]. Appl Surf Sci, 2011, 257: 2731. doi: 10.1016/j.apsusc.2010.10.053

[11]

Zhou H B, Zhang H Y, Tan M L. Effects of substrate temperature on the efficiency of hydrogen incorporation on the properties of Al-doped ZnO films[J]. Superlattice Microst, 2012, 51: 644. doi: 10.1016/j.spmi.2012.03.003

[12]

Moon Y K, Bang B, Kim S H. Effects of working pressure on the electrical and optical properties of aluminum-doped zinc oxide thin films[J]. J Mater Sci-Mater El, 2008, 19: 528. doi: 10.1007/s10854-007-9375-5

[13]

Kar J P, Kin S, Shin B. Influence of sputtering pressure on morphological, mechanical and electrical properties of Al-doped ZnO films[J]. Solid State Electron, 2010, 54: 1447. doi: 10.1016/j.sse.2010.07.002

[14]

Shin B K, Lee T I, Kar J P. Effect of deposition power on structural and electrical properties of Al-doped ZnO films using pulsed direct-current magnetron sputtering with single cylindrical target[J]. Mat Sci Semicon Proc, 2011, 14: 23. doi: 10.1016/j.mssp.2010.12.013

[15]

Kuo S Y, Liu K C, Lai F I. Effects of RF power on the structural, optical and electrical properties of Al-doped zinc oxide films[J]. Microelectron Reliab, 2010, 50: 730. doi: 10.1016/j.microrel.2010.01.042

[16]

Rech B, Remann T, Donker M N. Challenges in microcrystalline silicon based solar cell technology[J]. Thin Solid Films, 2006, 511/512: 548. doi: 10.1016/j.tsf.2005.12.161

[17]

Chang P K, Lu C H, Yeh C H. High efficiency a-Si:H/a-Si:H solar cell with a tunnel recombination junction and a n-type μ c-Si:H layer[J]. Thin Solid Films, 2012, 520: 3684. doi: 10.1016/j.tsf.2011.12.083

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Z F Lei, G Y Chen, S B Gu, L L Dai, R Yang, Y Meng, T Guo, L W Li. Development of aluminum-doped ZnO films for a-Si:H/μc-Si:H solar cell applications[J]. J. Semicond., 2013, 34(6): 063004. doi: 10.1088/1674-4926/34/6/063004.

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Manuscript received: 22 October 2012 Manuscript revised: 18 January 2013 Online: Published: 01 June 2013

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